It is desirable to carry out combustion, such as in incineration, with as high a throughput as possible so as to enhance the economics of the incineration process while achieving high combustion efficiency. A known method for increasing efficiency is to employ pure oxygen or oxygen-enriched air as the oxidant. The throughput of an incineration system is often limited by the volumetric flow rate of the flue gas. Since incineration with pure oxygen or oxygen-enriched air generates significantly lower volumes of flue gas for any given amount of combustion, such use increases the incinerator throughput and thus the overall efficiency of the incineration process.
A problem however with the use of pure oxygen or oxygen-enriched air in a combustion process is the high temperatures at which such combustion is carried out. This problem is especially evident in an incineration process wherein the waste to be incinerated has a high heating value such as one exceeding 3000 BTU/lb. The high temperatures may cause damage to the refractory, and may cause the excessive generation of harmful pollutants such as nitrogen oxides, commonly referred to as NO.sub.x.
It is known to use indirect heat sinks such as a water jacket wall to control the temperature within a combustion zone. However, such indirect heat sinks are generally mechanically complex. In addition, the cooled wall creates layers of cold gases which tend to deteriorate the organic chemical destruction efficiency of an incineration process. Furthermore, waste to be incinerated normally contains chlorine and/or sulfur compounds which form combustion products which can be very corrosive to the heat transfer surfaces.
Another known method for controlling the temperature within a combustion zone is to provide gas ballast, such as air, to the combustion zone. Unfortunately this method increases the flue gas volume and thus decreases the throughput thus negating some of the advantages of the oxygen or oxygen-enriched air combustion.
It has been proposed to use water as a heat sink within an incinerator combustion zone for temperature modification when the temperature reaches a predetermined high temperature setpoint. This is desirable because water vapor contains approximately twice the enthalpy per unit volume as does nitrogen at incineration temperatures and thus the throughput of the incinerator would undergo much less of a negative impact. However, the sudden injection of water may cause a temporary loss of vacuum. Unfortunately heretofore the use of water as an incinerator heat sink has failed to avoid the increase in the level of NO.sub.x generation and the poor temperature uniformity associated with a high oxygen environment, thus reducing the desirability of its use. In addition water spray may cause damage due to uneven cooling of refractory, and may also cause quenching of the combustion reaction.
Accordingly, it is an object of this invention to provide a combustion process which can employ pure oxygen or oxygen-enriched air as the oxidant and which employs a liquid heat sink while avoiding certain disadvantages presently associated therewith.